1. Field of the Invention
The present invention relates broadly to continuous tank-type regenerative glass melting furnaces, and more particularly to an improved regenerator system for such furnaces.
2. Description of the Prior Art
Large, high capacity continuous melting furnaces of the tank type employed in producing flat glass have generally included a number of burner ports spaced along either side at the upstream or charging end of the furnace. Conventionally, five to seven such ports may be employed, with each set of ports being connected to an associated regenerator extending along side the tank. The system is periodically cycled or reversed so that alternately, heated exhaust gases are withdrawn through the set of ports to store heat in the associated checkerbrick structure of the regenerator, or so-called checkers, and then combustion air is forced through the checkers to absorb the stored heat and thus be preheated prior to admission to the furnace melting zone through the ports.
Heretofore, conventionally in such furnaces combustion air has been admitted and exhaust gases withdrawn through tunnels extending throughout the length of and lying beneath the checkerwork structure of the regenerators. More particularly, due to the width of the regenerators the tunnel was provided with a longitudinally extending center support wall upon which transverse rider arches were supported for carrying the checker structure thereabove. The combustion air was introduced to and the exhaust gases were withdrawn from the tunnels at the upstream or charging end of the furnace.
Although the tunnels extend throughout the entire length of the regenerators on each side of the furnace, it has been found that because of flow characteristics including the tendency for the gases to follow the path of least resistance through the checkers, withdrawal of hot exhaust gases is predominantly through the upstream end of the regenerators. Conversely, as colder incoming combustion air is admitted to the tunnel, it travels predominantly to the far or downstream end of the regenerators. Thus, there is a tendency to create non-uniform gas flow and temperature patterns along the length of the regenerators. This compounding effect, wherein a disproportionate share of the hot combustion gases is withdrawn through the checkers in the vicinity of the first port while a disproportionate share of the cooling combustion air is drawn through the checkers in the vicinity of the last port, tends to create a temperature gradient within the checkers whereby the temperature at the upstream end, that is, in the vicinity of the first port, is considerably higher than at the downstream end.
Such a condition may both reduce the thermal efficiency of the furnace and accelerate deterioration of the regenerators due to abnormally high localized temperatures. Thus, due to the concentration of stored heat in certain areas and consequent deficiency of stored heat in other areas, the efficiency with which the combustion air is preheated and the fuel is utilized during the firing cycle is reduced. Also, the areas of high exhaust gas flow are subjected to excessive batch dust carryover from the tank, whereby some of the passages in the checkers may eventually become blocked, while the areas of lower brick temperatures are more susceptible to damaging sodium sulfate condensation.
Various schemes have been proposed for alleviating this problem. For example, particularly in connection with smaller furnaces as employed in the container industry, it has been proposed to subdivide the regenerators by vertical walls to, in effect, provide a separate regenerator chamber for each port or small group of ports. U.S. Pat. No. 4,174,948, issued Nov. 20, 1979 to Bradley et al., suggests separate intake air and exhaust gas manifolds extending along each regenerator, with branch ducts to the tunnel beneath each port, and valve or damper means in each branch duct which cycle upon each reversal of firing to regulate the flow of combustion air and exhaust gas through the associated checkers. In commonly assigned application Ser. No. 123,559 of Stover et al., filed Feb. 22, 1980, there is disclosed the concept of admitting combustion air at both ends of the tunnel beneath the checkers whereby the opposed flow tends to equalize operating temperatures throughout the length of the regenerator. While these and other prior art proposals have been beneficial in many instances, they have not entirely alleviated the problem.